1. Field of the Invention
The invention relates to a turbulence-free camera with enhanced spatial resolution and full color reproduction.
In 1956, astrophysicists Hanbury Brown and Twiss (HBT) invented the intensity interferometer and achieved a much more accurate measurement on the angular size of distant stars. Unlike the Michelson stellar interferometer, which measures the first-order interference of electromagnetic fields at a local point, the HBT interferometer measures the second-order intensity correlation of thermal light with two independent photodetectors placed at distant space-time coordinates. The joint-photodetection circuit outputs a nontrivial 1+(sin x/x)2 correlation function while scanning the relative transverse position of the two photodetectors. When the relative transverse position close to “zero”, i.e., x˜0, the intensity correlation function reaches its maximum value that is 50% greater. Taken the advantage of the intensity correlation of light coming from distant stars, HBT measured the angular diameter of the star and the angular separation between double stars that are uneasy to measure by other traditional astrophysical methods. Besides its useful applications, HBT's discovery was significant both conceptually and fundamentally. The HBT effect immediately provoked a debate on the classical or quantum nature of the phenomenon. It was this debate that stimulated the research on the basic concepts of the modern quantum theory of light. The discovery of HBT effect is a milestone in the history of modern quantum optics.
In the view of the inventors, the HBT effect is a two-photon interference phenomenon: a pair of random distributed and random radiated photons interferes with the pair itself. The two-photon interference “forces” the random photon pair to be correlated in transverse position, i.e., if one photon is observed at a position the other one has 50% more chance to be observed at a unique position simultaneously.
The HBT effect eventually spurred research into imaging technologies that take advantage of the point-to-point intensity correlation. As we understood the traditional imaging technology is based on a point-to-point correlation between the object plane and the image plane, namely the image-forming function: light coming from a point of the object plane can only be “seen” at a unique point on the image plane. In the view of the inventor, if a random pair of photons has 50% more chance to be observed at a point of the object plane and simultaneously at a unique point on a distant plane, namely the image plane, an image of the object will be obtained from a coincidence measurement of the photon pair. This thought of the inventor lead their research into the mechanism that would become known as “ghost imaging”, a technique that produces an image of an object by combining information from two photodetectors: a conventional, multi-pixel detector that does not view the object (usually a CCD camera), and a “bucket” single pixel detector that does view the object, however, cannot distinguish light that coming from different points of the object.
In fact, the first experimental demonstration on ghost imaging, which was published in an 1995 article by Pittman, Shih, Strekalov, Sergienko, “Optical imaging by means of two-photon quantum entanglement,” Phys. Rev. A 52 (1995), R3429, incorporated herein in its entirety, was not using thermal light. These experiments measured the coincidence of a quantum mechanically entangled photon pair, referred to as the signal and idler photon, respectively. The signal-idler pair has 100% chance to be located at a pair of two positions. In these ghost imaging experiments, after passing a lens, the signal photon either hit or passed through an object and then was detected by a bucket detector that measured only whether, but not where, the signal photon hit. At the same time, the idler photon propagated from the source directly to a CCD camera that recorded the actual position the idler photon hit. The coincidence counting rates between the bucket detector and the CCD camera were then recorded by a personal computer pixel by pixel. A 100% contrast image of the object was then observed from the coincidences.
From 2004, the inventors started to demonstrate thermal light ghost imaging by using randomly paired photons, instead of entangled photon pairs. The first a few publications includes: (1) A. Valencia, G. Scarcelli, M. D'Angelo, and Y. H. Shih, “Two-photon Imaging with Thermal Light”, Phys. Rev. Lett., 94, 063601 (2005); (2) G. Scarcelli, V. Berardi and Y. H. Shih, “Can Two-Photon Correlation of Chaotic Light Be Considered as Correlation of Intensity Fluctuation?” Phys. Rev. Lett., 96, 063602 (2006); (3) R. E. Meyers, K. S. Deacon, and Y. H. Shih, “Ghost Imaging Experiment by Measuring Reflected Photons”, Phys. Rev. A 77, Rapid Comm., 041801(2008). These articles are incorporated herein in its entirety. In the thermal light ghost imaging experiments, a photon either hit or passed through an object and then was detected by a bucket detector that measured only whether, but not where, that photon hit. At the same time, its random partner propagated from the source directly to a CCD array that recorded the actual position the photon hit. The CCD is placed at a distance from the light source that equals the distance between the light source and the object. The coincidence counting rates between the bucket detector and the CCD camera were then recorded by a personal computer pixel by pixel. A 50% contrast image of the object was then observed from the coincidences.
In 2011, we found and immediately demonstrated the HBT intensity correlation and thus the ghost imaging, is naturally turbulence-free. The published article by R. E. Meyers, K. S. Deacon, and Y. H. Shih, “Turbulence-free Ghost Imaging”, Applied Phys. Lett., 98, 111115 (2011), is incorporated herein in its entirety.